docs: def src_filter(self):
          """
          :returns: a SourceFilter/UcerfFilter
          """
          oq = self.oqparam
          self.hdf5cache = self.datastore.hdf5cache()
          sitecol = self.sitecol.complete if self.sitecol else None
          if 'ucerf' in oq.calculation_mode:
              return UcerfFilter(sitecol, oq.maximum_distance, self.hdf5cache)
          return SourceFilter(sitecol, oq.maximum_distance, self.hdf5cache)